Preparation of alkyl substituted boron hydrides



f at ented PREPARATION OF ALKYL SUBSTITUTED BORON HYDRIDES Myrl Lichtenwalter and Kenneth E. Harwell, Austin,

Tex., assignors to Callery Chemical Company, Pittsburgh, Pa., a corporation of Pennsylvania No Drawing. Filed Mar. 6, 19'56, Ser. No. 569,945

3 Claims. (Cl. 260606.5)

This invention relates to the preparation of a liquid h gh energy fuel composition comprising alkyl substituted higher boron hydrides and more particularly to their preparatron by the reaction of alkyl diboranes with pentaborane-9 (B H Since pentaborane-9 can be prepared by a variety of well known methods and since alkyl diboranes such as diethyl diborane can be prepared by the reaction of ethyl,- ene with diborane, it appeared likely that alkyl substituted higher boron hydrides could be prepared from higher boron hydrides which would have certain desirable properties. It is an object of this invention to provide a new and improved method for the preparation of fuel mixtures comprising alkyl substitutedhigherboron hydrides by the reaction of alkyl diboranes with pentaborane-9.

Other objects of this invention will become apparent as described in the specification and the claims hereinafter related. 7

This new and improved method of preparing liquid high energy fuel mixtures will be described more fully in the specification and the novelty thereof will be particularly pointed out and distinctly claimed.

This invention is based upon our discovery that liquid products having desirable chemical and physical properties for use as high energy fuels can be prepared by the reaction between a lower alkyl diborane and penta borane-9.

In a series of experiments diethyl diborane was refluxed with pentaborane-9 for 30 to 240 minutes at a liquid temperature of 25 to 65 C. at a pressure of 70 to 675 millimeters of mercury. The apparatus was arranged so that any diborane produced passed out of the system while higher boiling materials were returned to the reaction as reflux. The following results were obtained:

reacted pentaborane-9; fraction 2 was mainly unreacted d ethyl diborane; fraction 3 was a mixture of alkyl boranesconsisting primarily of alkyl higher boranes such as ethyl pentaboranes and contained 26.6 percent boron and 59.2

percent carbon. The spontaneous ignition temperature of the liquid reaction product obtained in these runswas 65-70 C. Other physical properties of the liquid reaction product obtained were: melting point =101 0., and n =l.4004.

The liquid products which are produced by the above reactions are useful as high energy fuels in bi-propellant systems. These liquid high energy fuels burn readily with conventional oxidizers, including air and oxygen, and are primarily useful in turbojet, ram jet, and rocket engines. These fuels may be used alone or in mixtures with other fuels toward which they are chemically inert, e.g. most ordinary hydrocarbon fuels. These fuels have a high heat of combustion (greater by 20-50% than the best hydrocarbon fuels), are spontaneously inflammable at high temperature, and have other desirable fuel properties such as low freezing point, large liquidus range, high density, and moderate resistance to hydrolysis. In actual tests, a sample of the fuel produced by the above process is introduced into the combustion section of a jet test engine, burned with compressed air, and the efiicency of the combustion and the output of the engine measured.

' When this fuel is burned in a test engine it has a heat of combustion more than 20% greater than the best hydrocarbon fuels. The combustion efliciency is equal to JP-4 .(a standard jet fuel in use for several years past) and the thrust of engine per unit weight of fuel is sub stantially greater than the thrust obtained using the best hydrocarbon fuels. In comparative tests on the fuel produced by the above process and other boron-containing high energy fuels and other hydrocarbon fuels, it has been found that engine output is directly propertional to the heat of combustion per unit weight of fuel. Thus, an aircraft using a high energy boron-containing fuel can travel proportionately further with the same load or can carry proportionately greater loads, than when fueled with conventional fuels.

It should be understood that this invention embraces the reaction of other lower dialkyl diboranes with pentaborane-9 in addition to the reaction of diethyl diborane with pentaborane-9.

While we have described several embodiments of our invention it is to be understood that within the scope of the claims appended hereto this invention may be practiced otherwise than as specifically described.

Analysis of Liquid Percent Reaction Product Run Mols Mols Reaction Temp., Pressure, Conver- No. EhB H, B 119 time 0. mm. slon (mlns) EtQBgH Wt. Wt.

Per- Per- H 1 cent, 13 cent, 0

1 H is the volume of hydrogen evolved in complete hydrolysis of the product expressed 11 mllllmols per gram of product.

In all of the above reactions the gases evolved were condensed in a trap immersed in liquid nitrogen. The

trap was then connected to an infra-red sample cell. The trap was warmed and the resulting gases were passed into the cell and analyzed. These condensed vapors were mainly diborane with some unreacted ethyl diboranes. The liquid product obtained in each case was separated into three fractions by distillation. Vapor pressure and boron analyses indicated that the fraction 1 was mainly unprises contacting a lower alkyl dihoraqe 1 with genteborane-9 at reaction conditions of temperature and pressure and recovering the liquid product thus formed.

2. A method according to clairrrl in which the alkyl diborane is arr ethyl diborane. t

3. A method accordirag to claim 1 in which the alkyl removed is the more volatile product; arid the liquid comprising a mixture of alkyl substituted higher boron hydrides is recovered as the less volatile product.

No references cited. 

1. A METHOD OF PREPARING A LIQUID HIGH ENERGY FUEL MIXTURE COMPRISING LOWER ALKYL SUBSTITUTED HIGHER BORON HYDRIDES CONTAINING 25 TO 55% BORON BY WEIGHT WHICH COMPRISES CONTACTING A LOWER ALKYL DIBORANE WITH PENTABORANE-9 AT REACTION CONDITIONS OF TEMPERATURE AND PRESSURE AND RECOVERING THE LIQUID PRODUCT THUS FORMED. 